This invention relates in general to warning systems and, in particular, to a low drag warning system for emergency vehicles.
More specifically, but without restriction to the particular use which is shown and described, this invention relates to an improved low drag warning system with speaker employing low drag light domes and a center siren housing having a surface designed to deflect air flow beneath the housing for less turbulence and drag. The system herein disclosed is provided with sound means by which improved sound characteristics are accomplished with a relatively small driver. The invention of the application includes means to circulate a flow of air through the lighting globes in a manner to prevent condensation and effect cooling of the components.
Warning light and siren systems for emergency vehicles generally are designed to project above the roof line of the vehicle. The presence of a housing on the roof of a vehicle inherently imposes air drag which causes the engine to operate with less fuel economy and performance. The speaker housing has been one of the primary sources of air drag in warning systems for emergency vehicles, since it must enclose a speaker having a size sufficient to meet sound standards dictated by various states, particularly stringent in California.
Even the most streamlined of prior art warning systems produces a significant amount of drag due to the turbulence created in the air flow. Prior designs having both lighting globes and a suitable sound system capable of meeting state standards may generate a drag greater then ten pounds at fifty miles per hour with a typical 48" long housing. The imposition of an additional load of this magnitude interferes with the efficient operation of the vehicle. Known designs are also subject to deficiencies in design which prevent extended service-free operation. The formation of condensation in the globe compartment can deteriorate the components as can the build-up of heat. Typical warning systems fail to attack these problems by a simple and straightforward technique.
An emergency system must meet stringent standards of sound propagation to be used in many applications, such as in police vehicles. For certain uses, the State of California, for example, requires an output of sound of 120 decibels at approximately 10 feet in front of speaker and 113 dB at .+-.50.degree. points. To meet this and other similar standards in various jurisdictions, known speakers have required two high powered, 100 watt drivers.